The present invention relates to the treatment of cardiovascular disease. More specifically, the present invention relates to an apparatus and method for angioplasty that prevents re-stenosis.
Cardiovascular disease is the leading cause of death in the United States. Arteriosclerosis refers generally to a group of diseases in which the lumen of an artery becomes narrowed or blocked (occluded). The narrowing of the artery restricts blood flow to the organ that is nourished by the artery. The reduced blood flow results in the deterioration of the organ to the point wherein the organ can be permanently damaged unless the blockage of blood flow is removed.
When an artery that serves the heart is narrowed or blocked, this pathological process results in a heart attack. A variety of therapies have been developed to prevent heart attacks and to restore adequate blood flow to the heart. These therapies include dilating the artery utilizing a pharmaceutical, surgical intervention by replacing the blocked segment with a new segment (or coronary artery by-pass graft), or the use of a catheter-mounted mechanical device, such as a balloon.
Although in most cases, surgery is required to reestablish an occluded lumen to proper diameter, by-pass surgery and the like presents a number of disadvantages to the patient. By-pass surgery is quite expensive, creates a period of discomfort for the patient, and involves the surgical risks associated with any major surgery. Therefore, the focus recently has been on relatively noninvasive and less risky alternatives to conventional surgery.
One such method is known as angioplasty, or when used with coronary arteries, percutaneous transluminal coronary angioplasty. Generally, angioplasty is performed using a multilumen inflatable balloon catheter. At least one lumen of the catheter is open ended and allows the passage of a guide wire, or in some instances, the direct intra-arterial infusion of a pharmaceutical agent therethrough. In angioplasty, the guide wire is directed to the area of arterial narrowing using x-ray monitoring, for example, a roentgengraph or fluoroscope. Thereafter, the catheter is positioned with the aid of the guide wire in the region of arterial narrowing.
Concentric with the lumen that includes the guide wire is a second lumen that is connected to an elongated inflatable segment or balloon portion. This balloon portion is located near the distal end of the catheter and is constructed from a material having a high tensile strength and low elasticity. The second lumen and balloon are generally filled with diluted contrast medium. The contrast medium is a radiopaque liquid that makes the visualization of the catheter possible by fluoroscopy.
The typical angioplasty procedure involves the introduction of the catheter into the arterial system of the patient, for example, through the femoral artery of the leg. The catheter is then guided to the affected artery, for example, the left anterior descending coronary artery, manually with the aid of fluoroscopy.
Once the catheter is appropriately positioned in the affected artery, the guide wire is advanced to and past the point of obstruction. The balloon portion of the catheter, which surrounds the guide wire, is thereby advanced along the guide wire until it is in juxtaposition to the occluded segment. The balloon is then inflated. As the balloon expands, it pushes the occluding tissue toward the walls of the vessel. This correspondingly increases the diameter of the occluded artery.
Typically, the balloon is inflated and deflated a number of times. By repeatedly inflating and deflating the balloon, it is hoped that the corresponding repeated deformation of the occluding tissue will permanently deform the tissue thus providing the affected artery with a lumen having a sufficiently large inner diameter.
After the balloon has been inflated and deflated an arbitrary number of times, the balloon is then collapsed and retracted. The site of obstruction is then examined angiographically. This is often performed by injecting a radiopaque dye through the lumen housing the guide wire. If the artery is still occluded, the procedure is repeated.
Examples of such catheters include Medtronic Thruflex and Advanced Cardiovascular Systems catheters.
The popularity of angioplasties has increased dramatically. In the United States in 1989, hundreds of thousands of angioplasties were performed. This number is rapidly increasing. Fortunately, for many patients, angioplasty permanently reopens the previously occluded arteries. However, in 30% of the occluded arteries which are opened by an angioplasty technique, the arteries re-occlude within six months of the procedure. This results in symptoms of cardiac ischemia, such as chest pain, exercise intolerance, and shortness of breath. The patient's risk of disabling or fatal heart attack is markedly increased.
It is believed that re-stenosis in a previously treated segment of an artery is due to the stretch-induced damage of arterial tissue. The response to the damage caused by the inflation of the balloon catheter is an exaggerated healing response that includes proliferation of the undamaged tissue. The proliferating tissues are the endothelial cells that form the lining of the lumen and fibroblasts and smooth muscle cells that reside in the artery wall.
In attempting to prevent re-stenosis from occurring, vascular stents have been installed within the artery for the purpose of holding the lumen open. However, this has been found to be an unsatisfactory solution since proliferating tissue will grow around and through the stent lattice re-occluding the lumen. Accordingly, there is a need for preventing or reducing restenosis in arteries that have undergone angioplasty.